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July 29, 1924 1502.875

M. I. PUPIN ET AL TONE PRODUCING RADIORECEIVER Filed Feb. 10, 1916 2 Sheets-Sheet L nvenfow vmfifza x $51 wattozmeq July 29, 1924.

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. iJLT J rpgm w: il l hw J0EE? E L T rzpg gf Patented July 29, 1924.

. UNITED STATES 1,502,875 PATENT OFFICE.

MICHAEL L PUPIN, OF NORFOLK, CONNECTICUT, AND EDWIN H. ARMSTRONG, O'F YONKERS, NEW YORK, ASSIGNORS TO WESTINGHOUSE ELECTRIC AND MANUFAC TUBING COMIANY, OF EAST PITTSBURGH,

PENNSYLVANIA.

PENNSYLVANIA, A CORPORATION OF TONE-PRODUCING BADIOR-ECEIVER.

Application flied February 10, 1916. Serial No. 77,436.

To all whom it may concern:

Be it known that we, MICHAEL 1. Form, a citizen of the United States, residing in Norfolk, county of Litchfield, State of Connecticut, and EDWIN H. ARMSTRONG, a citizen of the United States, residing in Yonkers, county of Westchester, State of New York, have invented certain new and useful Improvements in Tone-Producing Radioreceivers; and we do hereby declare the following to be a full, clear, and exact description of the invention, such as will enable others skilled in the art to which it appertains to make and use the same.

The object of this invention is the reception of continuous waves by means of a new form of tone producing apparatus in which an electrical amplifier is arranged to repeat the incoming waves at an am litude which varies periodically at an audi 1e frequency so that the resultant electric waves produce a. musical note in any ordinary receiving system. The modification in amplitude is most conveniently produced by means of a vacuum tube repeater-amplifier which re posts the incoming high frequency oscillations from the antenna to the usual receiving apparatus, but which repeats only at eriodic intervals or with an amplitude w ich varies periodically with time so that the in comin oscillations of continuous amplitude are de ivered to the receiver as amplified oscillations of thevsame frequency but periodically varying in amplitude, the period of these variations being at an audible frequency.

Referring to the diagrams which form a part of this s ecification,

Figurel il ustrates a means of securing the required periodic variations in the amplitude of the repeated signal by means of an alternator as hereinafter described,

Fig. 2 illustrates a method of securing the desired variation automatically by means of the tube itself;

Fig. 3 and Fig. 4 show methods of protecting the detector and telephone or similar translating device from the direct effect of the local frequency which may, under certain conditions, produce a continuous tone in the telephone.

Referring now to Fig. 1, 1 is a vacuum tube repeater havin in its output circuit an alternator 2; and 3 represents any suitable detecting translating device associated with the output circuit of the relay as shown. In this diagram, as in the other diagrams of the drawings, the means for detecting the received signals is illustrated as a rectifying detector 16 associated .with a pair of telephones 1?, but it will be understood that any suitable detecting means may be e1nployed, and that when in the specification and claims we refer to an oscillation responsive device, we intend to include this detecting arrangement as well as any equivalent thereof.

The production of a tone for continuous waves is accomplished as foliowsIt is well known that the various types of vacuum tubes will reproduce at greater amplitude electric waves impressed on the exciting side of the tube and that this amplification ratio will be constant if the steady value of thermionic current through the tube is not changed, Under these conditions with a tube arranged to repeat from an antenna to an ordinary receiving system continuous waves of constant amplitude impressed on the antenna will be reproduced exactly in the receiving circuit. As these waves are of constant amplitude there will be no appreciable response in the telephones. If, however, the thermionic current is varied peri odically at some audible frequency the amplification ratio of the tube will vary periodically at the same frequency so that continuous oscillations of constant amplitude in the antenna are repeated to the receivin circuit as amplified oscillations of periodically varying amplitude. By varying the thermionic current at a suitable frequency the sig nal produces any desired musical tone in the telephones.

The variation in the thermionic current and consequently in amplifying ratio may be obtained in several other ways, as, or in stance, heating the filament by an alternatingcurrent or, in the three-electrode tubes, by connecting the alternator in the grid cir cuit so that it varies the wing current indirectly by varying the rid potential. The manner of operation of any of the methods is obvious from the foregoing explanation. It should here be noted that the receiver opcrates most effectively when the thermionic current, at those times when it is reduced to its lowest value, approaches as nearly as pos tutc sible to zero. For this reason the use of alternating current to heat the filament is not as c'lfcctive as one of the other methods, as the temperature of the filament does not vary between sufficiently wide limits when the frequency of the heating current is within the range of good audibility.

The amplifying ratio may be varied automatically by the tube itself and-the alternator dispensed with. This result is accomplished by the system of Fig. 2 in which the tube t is arranged with a reaction circuit 5, 6, 7, 8 which causes the system to oscillate continuously at a suitable low frequency. This he uency is determined by the constants of the capacity of the condensers 5, 8, By adjustment of these condensers the local frequency is regulated to produce a variation in the thermionic current of any desired audible frequency. The behavior of the rest. of the system in regard to the signallingfre uency is the same as for the system of 1g. 1.

It is advisable to protect the receiving circuits from the effects of the local frequency which tends to produce a continuous tone in the telephone and a method of accomplishing this is shown by Fig. 3. Two tuned paths l-1l and 12-13 selective respectively to the low and high frequencies are connected in parallel as shown. The two frequencies are thereby separated and the receiving circuit effectively shielded. As an additional precaution the adjacent ends of the. transformer 11-13 may be grounded as illustrated to guard. against capacity currents between them through the telephones to earth. An improved substifor the selective path 12-l3 is illustrated by Fig. e in which the output circuit of the repeater is connected'with the receiving apparatus by means of a selective path consisting of an artificial line 15 of the type illustrated in the drawing. The line consists of several equal elements, each comprising a capacity 18 shunted by an inductance '19, the inductance and capacity of each element being so adjusted that the element fulfills the conditions of resonance tie transformer 6. 7 andfor a frequency about %higher than the fretpuency of the. incoming signalling waves. sue: a line will transmit efliciently the high frequency of the incoming waves but will wip out completely the local low frequency.

What we claim is:

1. A receiver for continuous high-fie quency electric waves comprising a wave conductor, an electrical repeater, including a means for producing a local frequency, an oscillation-responsive device connected to the output circuit of'the repeater through an artificial, line which has a high attenuation constahtrtor the local frequency and a low attenuation constant for the signalling frequency, said artificial line being composed of a plurality oflilre units, each unitcomprising two impedances of unlike reactance and all of said units being similarly connected, said repeater being arranged to repeat electrical currents in the wave conductor into the oscillationresponsive device at a periodically varying amplitude.

12. Ina radio receivin system, a receiving circuit, a vacuum-tube evice coupled thereto, means associated with said device for producing a low-frequency modulation, an osciNation-responsive device and a highpass radio-frequency filter between said. as cillation device and said modulating means, comprising a plurality of .like units, each of said units having-a plurality of impedances, ofunlike 'nature,cimpedances of like nature being similarly situated in the several units.

3. In a radio signaling system, a vacuumtube device, a translating device and a filter coupling them, said filter-including a plurality of like units, each unit comprising two reactances of opposite sign, all the reaotances of one sign being connected in series and all thoseof the other sign in arallel, whereby the units form a chain extending the len th of the filter.

In testimony w liereof We afiix our signatures.

MICHAEL I. PUPIN. EDWIN H. ARMSTRONG. 

